Trona-enhanced steam foam oil recovery process

Abstract

In a continuous or cyclic steam foam drive, recovery of an acidic reservoir oil (1) is improved by injecting steam accompanied by (a) enough dissolved alkaline monovalent salt to ion-exchange multivalent cations from the reservoir rocks and precipitate those ions in compounds which are insoluble in an alkaline aqueous liquid as well as forming soaps of the reservoir oil acids and (b) surfactants for foaming the steam and increasing the salt tolerance of an aqueous surfactant system containing the soaps of the reservoir oil acids, and (2) is further improved by using trona or an equivalent mixture of alkali metal carbonates and bicarbonates as the alkaline monovalent salt.

What is claimed is: 
     
       1. In a process in which steam and steam-foaming surfactant are injected into a subterranean reservoir for displacing a relatively acidic oil toward a production location, which process includes injecting into the reservoir, at least as soon as at least some portion of the steam is injected, (a) a kind and amount of water soluble, alkaline material effective for ion-exchanging multivalent ions from the reservoir rocks and precipitating compounds containing those ions and for causing the aqueous liquid phase of the injected fluid to form soaps of substantially all of the petroleum acids in the reservoir oil, and (b) at least one surfactant arranged for foaming the steam and providing a preformed cosurfactant material capable of increasing the salinity requirement of an aqueous surfactant system in which soaps derived from the reservoir oil comprise a primary surfactant, an improvement comprising: using as said water soluble alkaline material, a material consisting essentially of a substantially equal molar mixture of alkali metal carbonates and bicarbonates which is, or is substantially equivalent to, trona.   
     
     
       2. The process of claim 1 in which part of said alkaline material is injected as a relatively concentrated aqueous solution before injecting the steam. 
     
     
       3. The process of claim 1 in which a portion of steam is injected so that it forms a steam zone within the reservoir, at least one portion of said alkaline material is injected into the reservoir as a component of a relatively concentrated aqueous alkaline liquid mixed with steam and a preformed surfactant capable of functioning as said cosurfactant, and then, steam mixed with surfactant and a lower concentration of alkali is injected into the reservoir to provide an alkaline steam foam displacement of oil. 
     
     
       4. The process of claim 1 in which said surfactant comprises an olefin sulfonate surfactant capable of providing both the steam foaming and cosurfactant operations. 
     
     
       5. The process of claim 4 in which said alkaline material is a substantially equimolar of alkali metal carbonates and bicarbonates. 
     
     
       6. The process of claim 5 in which said alkali metal is sodium. 
     
     
       7. The process of claim 1 in which oil is recovered by a steam-foam soak process. 
     
     
       8. The process of claim 1 in which oil is recovered by a steam-foam drive process. 
     
     
       9. The process of claim 1 in which aqueous alkaline material and preformed cosurfactant are injected into the reservoir in the form of a steam-foam-forming mixture comprising steam, noncondensible gas, a steam-foaming surfactant inclusive of said preformed cosurfactant and an electrolyte which consists essentially of said alkaline material.